Hi,
Module Settings is a developer convenience for storing and retrieving key value pairs. I do not see any benefit to having events and providers to respond to events based on changes in module settings, it is just a storage mechanism like a dictionary that you can use if you want to and is convenient for many features because you don't need to create your own table or UI to manage settings there, but it is not meant to be a one size fits all solution for every need.
If you need more complex solution you can implement your settings in your own table and create your own business classes or pages with events. For example in WebStore I felt I needed more than what module settings provides so I implemented a StoreSettings on it's own Store table and a StoreSettings.aspx page to manage the settings. So far I have not needed it but I could implement a Store changed event if I needed it.
Hope it helps,
Joe